1. Field of the Invention
The present invention generally relates to computer networks, and more specifically to group-oriented multicast routing in an internetwork, wherein the reacheable extent of multicast packets is limited within an area, called "multicast scope".
2. Description of the Related Art
For multicast routing in an internetwork, the concept of "multicast scope" is described in a dissertation "Multicast Routing in a Datagram Internetwork" submitted to Stanford University, S. E. Deering, December 1991. An internetwork having a multicast scope (or simply scope) has the ability to limit the "scope" of a multicast transmission to reach only nearby destinations. As disclosed in "IP Version 6 Addressing Architecture" Request for Comment 1884, RFC 1884, December 1995, R. Hinden et al, a scope can be established by encapsulating a four-bit scope field in the address field of a multicast packet according to the internet protocol version 6. Using the scope field of a multicast packet, each router in the internetwork intercepts the packet and prevents it going beyond the boundary of the scope.
While there are a number of advantages for limiting the scope of a multicast, it is disadvantages for mobile hosts visiting a subnetwork external to the scope if they wish to, or are entitled to, participate in group activities within the scope. One approach is to encapsulate a multicast packet in the payload field of a unicast packet and send it from a home agent to an external mobile host. However, the number of unicast packets will increase with an increase in external mobile hosts, causing a significant increase in traffic.